Bite Angle Effects of κ²<i>P</i>‑dppm vs κ²<i>P</i>‑dppe in Seven-Coordinate Complexes: A DFT Case Study

This paper predicts the effects of replacing dppm (bis­(diphenylphosphino)­methane) with dppe (1,2-bis­(diphenylphosphino)­ethane) in seven-coordinate organometallic complexes by employing density functional theory (DFT) computations for a case example: WI₂(CO)­(κ²P-dppm)­(η²:η²-nbd) (nbd = norbornadiene), an intermediate in the W­(II)-catalyzed ring-opening metathesis polymerization (ROMP) of nbd. Effects on both structure and ligand binding energy (i.e., reactivity) were investigated. For the known W–dppm complex (crystal structure provided here), of 37 energy-distinct stereoisomers found, only one low-energy stereoisomer is predicted, and it agrees with the known X-ray crystal structure, lending faith to the conformer search procedure. For the as yet unknown W–dppe complex, of 31 energy-distinct stereoisomers found, two low-energy stereoisomers are predicted. The computed DFT ligand binding energies {W–P, W–ene, W–CO, W⁺–I^–} are {9, 17, 44, 102} kcal mol^–1 for the W–dppm complex and {3, 15, 37, 95} for the W–dppe complex. The conclusion is that the increased PWP bite angle of dppe vs dppm will reduce <i>all</i> ligand binding energies due to increased interligand steric repulsion